Plasmodium falciparum protein phosphatase PP7 is required for early ring-stage development

We previously reported that the Plasmodium falciparum putative serine/threonine protein phosphatase 7 (PP7) is a high confidence substrate of the cAMP-dependent protein kinase (PKA). Here we explore the function of PP7 in asexual P. falciparum blood stage parasites. We show that conditional disruption of PP7 leads to a severe growth arrest. We show that PP7 is a calcium-dependent phosphatase which interacts with calmodulin and calcium-dependent protein kinase 1 (CDPK1), consistent with a role in calcium signalling. Notably, PP7 was found to be dispensable for erythrocyte invasion, but was crucial for ring-stage development, with PP7-null parasites arresting shortly following invasion and showing no transition to ameboid forms. Phosphoproteomic analysis revealed that PP7 may regulate dephosphorylation of PKAc substrates, particularly in the presence of Ca2+. Its interaction with calmodulin and CDPK1 further emphasise a role in calcium signalling, while its impact on early ring development and PKAc substrate phosphorylation underscores its importance in parasite development.